Package with contoured seal

ABSTRACT

A packaged food article includes a meat product and a thermoplastic, heat shrinkable film. The film includes a meat-contact layer that contains a polymer which includes mer units derived from a C 2 -C 4  α-olefin. The film is sealed so as to form a bag which encloses the meat product. At least one of the seals defines an arc which includes at least four segments. Each of the segments has a radius of curvature which differs from the radius of curvature of any adjoining segment. When the packaged food article is subjected to a temperature of from about 50° C. up to about the Vicat softening point of the polymer of the meat-contact layer, the packaged food article takes the general shape of a poultry breast.

This application is the National Stage (35 U.S.C. §371) of InternationalApplication No. PCT/US99/05995 filed Mar. 18, 1999, which claims thebenefit of U.S. Provisional Application No. 60/080,098 filed Mar. 31,1998.

BACKGROUND INFORMATION

1. Field of the Invention

The present invention relates to packaged food articles, specificallyarticles where a food product is cooked after being packaged.

2. Background of the Invention

Many food products are processed in thermoplastic film packages bysubjecting the packaged product to elevated temperatures produced by,for example, immersion in hot water or exposure to steam. Such thermalprocessing often is referred to as cook-in, and films used in suchprocesses are known as cook-in films.

A food product that is packaged and processed in this manner can berefrigerated, shipped, and stored until the food product is to beconsumed or, for example, sliced and repackaged into smaller portionsfor retail display. Many sliced luncheon meats are processed in thisfashion. Alternatively, the processed food can be removed immediatelyfrom the cook-in package for consumption or further processing (e.g.,sliced and repackaged).

A cook-in film must be capable of withstanding exposure to rather severetemperature conditions for extended periods of time while notcompromising its ability to contain the food product. Cook-in processestypically involve a long cook cycle. Submersion in hot (i.e., about 55°to 65° C.) water for up to about 4 hours is common; submersion in 70° to100° C. water or exposure to steam for up to 12 hours is not uncommon,although most cook-in procedures normally do not involve temperatures inexcess of about 90° C. During such extended periods of time at elevatedtemperatures, any seams in a package formed from a cook-in filmpreferably resist failure (i.e., pulling apart).

The cook-in film preferably possesses sufficient adherence to the foodproduct to inhibit or prevent “cook-out” (sometimes referred to as“purge”), which is water and/or juices that collect between the surfaceof the contained food product and the food-contact surface of thepackaging material during the cook-in process. Preventing cook-out canincrease product yield, provide a better tasting product, improve shelflife and provide a more aesthetically appealing packaged product. Filmsthat adhere well to the packaged food product help reduce cook-out.

Many cook-in films are corona treated to increase the surface energy oftheir food-contact layers. However, corona treatment can beinconsistent, can result in a film with inconsistent adhesion, canresult in a film having a surface energy that decays over time, and caninterfere with the sealability of a film.

Following the cook-in process, the film or package preferably conforms,if not completely then at least substantially, to the shape of thecontained food product. Often, this is achieved by allowing the film toheat shrink under cook-in conditions so as to form a tightly fittingpackage. In other words, the cook-in film desirably possesses sufficientshrink energy such that the amount of thermal energy used to cook thefood product also is adequate to shrink the packaging film snugly aroundthe contained product. Alternatively, the cook-in film package can becaused to shrink around the contained food product prior to initiatingthe cook-in procedure by, for example, placing the package in a heatedenvironment prior to cooking.

Some presently available cook-in films adhere well with the meat productand do a good job of reducing cook-out. Additionally, most such filmsare able to withstand extended time periods at the elevated temperaturesdescribed supra; accordingly such films are adequate for many cook-inapplications. However, some cook-in applications impose even morestringent performance requirements. For example, some food products thatare processed via cook-in procedures are oxygen sensitive. Cook-in filmsfor these products need to include one or more oxygen barrier layers.Other cook-in applications require that the film or the package madetherefrom be printable and be able to retain any image printed thereon.

An increasingly important requirement of cook-in films is that theyprovide an aesthetically pleasing packaged food product. For example, asmentioned previously, the cook-in film generally shrinks until it atleast substantially conforms to the shape of the enclosed food product;however, unless the shape of that food product is itself aestheticallypleasing, the resulting packaged food article does not have anaesthetically pleasing shape.

Because pre-forming the food article prior to packaging is impractical(and often impossible), providing a cook-in film that can provide aresulting packaged food article with an aesthetically pleasing shape ishighly desirable.

SUMMARY OF THE INVENTION

Briefly, the present invention provides a packaged food article whichincludes a meat product and a thermoplastic, heat shrinkable film. Thefilm includes a meat-contact layer that contains a polymer whichincludes mer units derived from a C₂-C₄ α-olefin. The film is sealed soas to form a bag which encloses the meat product. At least one sealededge of the bag defines an arc which includes at least four segments.Each of the segments has a radius of curvature which differs from theradius of curvature of any adjoining segment.

When the packaged food article is subjected to a temperature of fromabout 50° C. up to about the Vicat softening point of the meat-contactlayer polymer that includes mer units derived from a C₂-C₄ α-olefin,preferably up to about 100° C., the packaged food article advantageouslytakes the general shape of, for example, a poultry breast. Because thearc of the bag edge includes at least four segments with varying radiiof curvature, the general shape of the packaged food article is notessentially spherical. Rather, the packaged food article has a moreirregular, yet generally rounded appearance such as is observed inactual poultry breasts.

To assist in understanding the more detailed description of theinvention that follows, certain definitions are provided immediatelybelow. These definitions apply hereinthroughout unless a contraryintention is explicitly indicated:

“polymer” means the polymerization product of one or more monomers andis inclusive of homopolymers as well as copolymers, terpolymers,tetrapolymers, etc., and blends and modifications of any of theforegoing;

“mer unit” means that portion of a polymer derived from a singlereactant molecule; for example, a mer unit from ethylene has the generalformula —CH₂CH₂—;

“homopolymer” means a polymer consisting essentially of a single type ofrepeating mer unit;

“copolymer” means a polymer that includes mer units derived from tworeactants (normally monomers) and is inclusive of random, block,segmented, graft, etc., copolymers;

“interpolymer” means a polymer that includes mer units derived from atleast two reactants (normally monomers) and is inclusive of copolymers,terpolymers, tetrapolymers, and the like;

“polyolefin” means a polymer in which some mer units are derived from anolefinic monomer which can be linear, branched, cyclic, aliphatic,aromatic, substituted, or unsubstituted (e.g., olefin homopolymers,interpolymers of two or more olefins, copolymers of an olefin and anon-olefinic comonomer such as a vinyl monomer, and the like);

“(meth)acrylic acid” means acrylic acid and/or methacrylic acid;

“(meth)acrylate” means acrylate and/or methacrylate;

“anhydride functionality” means an group containing an anhydride moiety,such as that derived from maleic acid, fumaric acid, etc., whetherblended with one or more polymers, grafted onto a polymer, orpolymerized with one or more monomers;

“oxygen permeance” (in the packaging industry, “permeance” often isreferred to as “transmission rate”) means the volume of oxygen (O₂) thatpasses through a given cross section of film (or layer of a film) at aparticular temperature and relative humidity when measured according toa standard test such as, for example, ASTM D 1434 or D 3985;

“longitudinal direction” means that direction along the length of afilm, i.e., in the direction of the film as it is formed duringextrusion and/or coating;

“transverse direction” means that direction across the film andperpendicular to the machine direction;

“free shrink” means the percent dimensional change, as measured by ASTMD 2732, in a 10 cm×10 cm specimen of film when subjected to heat;

“shrink tension” means the force per average cross-sectional areadeveloped in a film, in a specified direction and at a specifiedelevated temperature, as the film attempts to shrink at that temperaturewhile being restrained (measured in accordance with ASTM D 2838);

as a verb, “laminate” means to affix or adhere (by means of, forexample, adhesive bonding, pressure bonding, corona lamination, and thelike) two or more separately made film articles to one another so as toform a multilayer structure; as a noun, “laminate” means a productproduced by the affixing or adhering just described;

“directly adhered,” as applied to film layers, means adhesion of thesubject film layer to the object film layer, without a tie layer,adhesive, or other layer therebetween;

“between,” as applied to film layers, means that the subject layer isdisposed in the midst of two object layers, regardless of whether thesubject layer is directly adhered to the object layers or whether thesubject layer is separated from the object layers by one or moreadditional layers;

“inner layer” or “internal layer” means a layer of a film having each ofits principal surfaces directly adhered to one other layer of the film;

“outer layer” means a layer of a film having less than both of itsprincipal surfaces directly adhered to other layers of the film;

“inside layer” means the outer layer of a film in which a product ispackaged that is closest, relative to the other layers of the film, tothe packaged product;

“outside layer” means the outer layer of a film in which a product ispackaged that is farthest, relative to the other layers of the film,from the packaged product;

“barrier layer” means a film layer capable of excluding one or moregases (e.g., O₂);

“abuse layer” means an outer layer and/or an inner layer that resistsabrasion, puncture, and other potential causes of reduction of packageintegrity and/or appearance quality;

“tie layer” means an inner layer having the primary purpose of providinginterlayer adhesion to adjacent layers that include otherwisenon-adhering polymers;

“bulk layer” means any layer which has the purpose of increasing theabuse resistance, toughness, modulus, orientability, etc., of amultilayer film and generally comprises polymers that are inexpensiverelative to other polymers in the film;

“seal layer” (or “sealing layer” or “heat seal layer” or “sealantlayer”) means

(a) with respect to lap-type seals, one or more outer film layer(s) (ingeneral, up to the outer 75 μm of a film can be involved in the sealingof the film to itself or another layer) involved in the sealing of thefilm to itself, another film layer of the same or another film, and/oranother article which is not a film, or

(b) with respect to fin-type seals, an inside film layer of a package,involved in the sealing of the film to itself;

as a noun, “seal” means a bond of a first region of a film surface to asecond region of a film surface (or opposing film surfaces) created byheating (e.g., by means of a heated bar, hot wire, hot air, infraredradiation, ultrasonic sealing, etc.) the regions (or surfaces) to atleast their respective softening points; and

“cook” means to heat a food product thereby effecting a change in one ormore of the physical or chemical properties thereof (e.g., color,texture, taste, and the like).

Some films, including many which are used in cook-in processes, areoriented prior to use. Orientation involves stretching a film at anelevated temperature (the orientation temperature) followed by settingthe film in the stretched configuration (e.g., by cooling). When anunrestrained, non-annealed, oriented polymeric film subsequently isheated to its orientation temperature, heat shrinkage occurs and thefilm returns almost to its original, i.e., pre-oriented, dimensions.

An oriented film has an orientation ratio, which is the multiplicationproduct of the extent to which the film has been expanded in severaldirections, usually two directions perpendicular to one another.Expansion in the longitudinal direction, sometimes referred to as themachine direction, occurs in the direction the film is formed duringextrusion and/or coating. Expansion in the transverse direction meansexpansion across the width of the film and is perpendicular to thelongitudinal direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an envelope from which can be formed oneembodiment of a package according to the present invention.

FIG. 2 is a perspective view of one embodiment of a package according tothe present invention.

FIG. 3 is a cross sectional view taken along section line 3—3 from FIG.2.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Films used in the food packaging industry can be categorized by thenumber of layers that make up the film. Some films are made from asingle polymer or blend of polymers and thus have only one layer.However, most films presently used include more than one layer, i.e.,are multilayer films. In general, the layers of a multilayer film can beclassified as inner or outer. Additionally, any number of tie layers canbe included.

With respect to films used for cook-in processes in general, one outerlayer acts as the meat-contact layer while the other acts as the outsidesurface of the film. The former serves as the inside layer of a packageformed from the film and is in direct contact with the packaged foodproduct. The latter provides abuse resistance and, where desired, asurface for printing.

In FIG. 1, envelope 10 is made from thermoplastic film material 12.Thermoplastic film material 12 can be a single- or a multilayer film aslong as the layer(s) included are adequate for the end use desired forenvelope 10 and the meat-contact layer of thermoplastic film material 12contains a polymer which includes mer units derived from a C₂-C₄α-olefin. Although thermoplastic film material 12 can be laminated,blown, or cast, it preferably is a coextruded, blown film which has beenoriented, most preferably biaxially oriented. Orienting involvesinitially cooling an extruded film to a solid state (by, for example,cascading water or chilled air quenching) followed by reheating the filmto within its orientation temperature range and stretching it. Thestretching step can be accomplished in many ways such as by, forexample, “blown bubble” or “tenter framing” techniques, both of whichare well known to those skilled in the art. After being heated andstretched, the film is quenched rapidly while being maintained in itsstretched configuration so as to set or lock in the oriented molecularconfiguration.

Thermoplastic film material 12 can have a longitudinal (L) directionfree shrink of at least 1%, and a transverse (T) direction free shrinkof at least about 1% (both measured at 85° C.). Where desirable for aparticular application, thermoplastic film material 12 can have a freeshrink (at 85° C.) in at least one of the L and T directions of at least2%, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%,even up to 50%. Thermoplastic film material 12 can be biaxially orientedand have a free shrink (at 85° C.) in each of the L and T directions offrom about 1 to about 20%, more preferably from about 2 to about 15%,and even more preferably from about 3 to about 10%, and a total freeshrink (L+T) of from about 2 to about 40%, preferably from about 2.5 toabout 30%, more preferably from about 3 to about 20%, and still morepreferably from about 5 to about 15%. For certain applications,orienting then heat setting or annealing thermoplastic film material 12so as to provide a T direction free shrink (at 85° C.) of less than 10%,more preferably less than 5%, can be preferred. Heat setting can beaccomplished at a temperature from about 60° to 200° C., preferably fromabout 70° to 150° C., and more preferably from about 80° to 90° C.

Thermoplastic film material 12 can have a shrink tension of at leastabout 700 kPa, preferably at least about 1050 kPa, and more preferablyat least about 1400 kPa. Additionally, it can exhibit a Young's modulus(measured in accordance with ASTM D 882) of at least about 200 MPa up toabout 1750 MPa. Certain preferred embodiments of thermoplastic filmmaterial can have a Young's modulus of at least about 250 MPA,preferably at least about 275 MPa, more preferably at least about 300MPa, and even more preferably at least about 350 MPa. Other preferredembodiments of thermoplastic film material 12 can have a Young's modulusof from about 275 to about 1000 MPa, preferably from about 285 to about825 MPa, and more preferably from about 300 to about 700 MPa.

Examples of polymers which can be used in the meat-contact layer ofthermoplastic film material 12 include, but are not limited to,ethylene/α-olefin interpolymers, propylene/α-olefin interpolymers,butene/α-olefin interpolymers, ethylene/maleic anhydride interpolymers,ethylene/C₃-C₁₈ unsaturated ester interpolymers, and ethylene/C₃-C₁₈ethylenically unsaturated acid interpolymers. Specific examples ofpreferred polymers include ethylene/vinyl acetate copolymer (EVA),propylene/ethylene copolymer, propylene/butene copolymer, andethylene/α-olefin interpolymers including mer units derived fromethylene and from one or more C₆ to C₁₂ α-olefins such as 1-butene,1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, and the like.

Heterogeneous ethylene/α-olefin interpolymers generally have a densityin the range of from about 0.86 g/cm³ to about 0.94 g/cm³ and can besub-categorized as follows:

linear low density polyethylene (LLDPE)—ethylene/α-olefin interpolymerswith densities of about 0.91 to about 0.93 g/cm³;

linear medium density polyethylene (LMDPE)—ethylene/α-olefininterpolymers having densities of from about 0.93 to about 0.94 g/cm³;

very low density polyethylene (VLDPE)—ethylene/α-olefin copolymers withdensities ranging from about 0.88 to about 0.91 g/cm³ (Dow Chemical Co.;Midland, Mich.); and

ultra-low density polyethylene (ULDPE)—ethylene/α-olefin copolymers withdensities ranging from about 0.88 to about 0.91 g/cm³ (Union CarbideCorp.; Danbury, Conn.).

In addition to the heterogeneous ethylene/α-olefin interpolymers justdescribed, homogeneous interpolymers can be used in the meat-contactlayer. These interpolymers differ structurally from heterogeneousethylene/α-olefin interpolymers in that they exhibit a relatively evensequencing of comonomers within a chain, a mirroring of sequencedistribution in all chains, and a similarity of chain lengths (i.e., anarrower molecular weight distribution). Furthermore, homogeneousinterpolymers typically are prepared using single-site type catalysts(e.g., metallocenes) rather than Ziegler-Natta catalysts. Examples ofcommercially available homogeneous interpolymers include metallocenecatalyzed EXACT™ linear ethylene/α-olefin copolymers (Exxon ChemicalCo.; Baytown, Tex.); TAFMER™ linear ethylene/α-olefin copolymers (MitsuiPetrochemical Corp.); and AFFINITY™ long-chain, branchedethylene/α-olefin copolymers (Dow Chemical Co.).

The meat-contact layer of thermoplastic film material 12 preferablyincludes one or more interpolymers of one or more C₂-C₄ α-olefins (i.e.,ethylene, propylene, and 1-butene, with ethylene and propylene beingpreferred) and one or more C₃-C₁₈ ethylenically unsaturated acids. Merunits derived from the C₃-C₁₈ ethylenically unsaturated acid(s)preferably make up at least 2 weight percent of the interpolymer. Usefulethylenically unsaturated acids have the general formula CH₂═CRCOOHwhere R is hydrogen or a C₁-C₁₅, preferably C₁-C₁₀, more preferablyC₁-C₅ alkyl, cycloalkyl, aryl, alkoxy, etc., group. The specificidentity of the R group is unimportant as long as it does not interferewith the ability of the ethylenically unsaturated acid to copolymerizewith the α-olefin. A preferred ethylenically unsaturated acid is(meth)acrylic acid, with acrylic acid being particularly preferred.Regardless of the identity of the α-olefin(s) and the unsaturatedacid(s), the resulting interpolymer preferably has a melt index of fromabout 0.25 to about 50, more preferably from about 0.5 to about 10, andstill more preferably from about 1 to about 5.

Because it is an inside layer, the meat-contact layer of thermoplasticfilm material 12 can be involved in the sealing thereof so as to formenvelope 10. (Sealing is discussed more fully infra.) Accordingly,inclusion of one or more polymers having a Vicat softening poin thatis/are high enough to withstand cook-in temperatures (i.e., a softeningpoint which is greater than the temperature at which the meat product isto be cooked) but low enough to seal easily when subjected to normalheat sealing conditions is preferred. Specifically, at least about 10%(by wt.), preferably at least about 25% (by wt.), more preferably atleast about 50% (by wt.), most preferably at least about 75% (by wt.) ofat least one polymer having a Vicat softening point of at least about70° C., preferably at least about 80° C., more preferably at least about85° C., even more preferably at least about 90° C., and most preferablyat least about 95° C., preferably is included in the meat-contact layer.

Of course, in addition to the polymer including mer units derived from aC₂-C₄ α-olefin, one or more other polymers can be included in themeat-contact layer of thermoplastic film structure 12. Examples of suchadditional polymers include those with mer units derived from(meth)acrylic acid and/or vinyl acetate. Examples of polymer blends fromwhich the meat-contact layer can be formed include, but are not limitedto, two or more ethylene/α-olefin interpolymers, an ethylene/α-olefininterpolymer and an ethylene/acrylic acid interpolymer, as well as anethylene/acrylic acid interpolymer and an ethylene/vinyl acetateinterpolymer. The ordinarily skilled artisan can readily recognize otherpotentially useful polymeric blends.

With respect to the α-olefin/unsaturated acid interpolymers discussedpreviously, for certain applications, those having a Vicat softeningpoint (V) defined by the formula

V≧111° C.-2.78° C.(m _(A))

where m_(A) is the percent of mer units in the interpolymer derived froman unsaturated acid, ranging from about 2 to about 25, preferablyranging from about 4 to about 15, more preferably ranging from about 6to about 12 (with all of the foregoing ranges being inclusive of the endpoint values), can be beneficial. The y intercept value of the Vicatsoftening point in the above formula more preferably is 113° C., evenmore preferably 115° C., yet more preferably 117° C., and mostpreferably 120° C. Examples of α-olefin/unsaturated acid interpolymerswhich satisfy the foregoing formula include NUCREL™ ARX 84-1 and ARX84-2 ethylene/acrylic acid copolymers (DuPont de Nemours; Wilmington,Del.), which exhibit Vicat softening points of about 97° C. and 100° C.,respectively. The former includes about 6% (by wt.) mer units derivedfrom acrylic acid, whereas the latter includes about 7% (by wt.) merunits derived from acrylic acid.

Because films with high surface energies normally adhere better to meatproducts, thermoplastic film material 12 preferably has a relativelyhigh surface energy, even in the absence of a surface treatment (e.g.,corona treating). Specifically, its surface energy preferably is atleast 0.0325 J/m², preferably at least 0.035 J/m², more preferably atleast 0.0375 J/m², even more preferably at least 0.040 J/m², and mostpreferably at least 0.0425 J/m².

If desired or if necessary to increase its adhesion to the enclosed meatproduct (not shown), the outer surface of thermoplastic film material 12can be irradiated and/or corona treated. The former involves subjectingthermoplastic film material 12 to radiation such as corona discharge,plasma, flame, ultraviolet, X-ray, gamma ray, beta ray, and high energyelectron treatment, any of which can alter the surface of the filmand/or induce crosslinking between molecules of the polymers containedtherein. The use of ionizing radiation for crosslinking polymers presentin a film structure is disclosed in U.S. Pat. No. 4,064,296 (Bornsteinet al.), the teaching of which is incorporated herein by reference. Thelatter technique involves bringing thermoplastic film material 12 intothe proximity of an O₂- or N₂-containing gas (e.g., ambient air) whichhas been ionized. Various forms of plasma treatment known to those ofordinary skill in the art can be used to corona treat the outer surfaceof thermoplastic film material 12. Exemplary techniques are describedin, for example, U.S. Pat. No. 4,120,716 (Bonet) and U.S. Pat. No.4,879,430 (Hoffman), the disclosures of which are incorporated herein byreference.

In some instances, the polymer(s) in the meat-contact layer whichprovide thermoplastic film material 12 with high surface energy also canhave the desired Vicat softening point (i.e., at least about 65° C.,preferably at least about 70° C., most preferably at least about 75°C.). Examples of such “dual purpose” polymers include the aforementionedNUCREL™ ARX 84-1 and ARX 84-2 ethylene/acrylic acid copolymers.

For some applications, forming envelope 10 from a thermoplastic filmmaterial having a low oxygen permeance can be preferred. Such filmmaterials, at about 23° C. and 0% relative humidity, preferably have anoxygen permeance of (in ascending order of preference) no more thanabout 150 cm³/m²·atm·24 hours, 125 cm³/m²·atm·24 hours, 100cm³/m²·atm·24 hours, 75 cm³/m²·atm·24 hours, 50 cm³/m²·atm·24 hours, 30cm³/m²·atm·24 hours, 20 cm³/m²·atm·24 hours, and 10 cm³/m²·atm·24 hours.Representative examples of polymers that can be helpful in providing athermoplastic film material with a low oxygen permeance includeethylene/vinyl alcohol interpolymers (EVOH), polyvinylidene chloride(PVDC), polyamides, polyesters, and polyalkylene carbonates. Preferredamong these are EVOH and polyamides, with the former being mostpreferred. In particular, EVOH having from about 32 to about 48 molepercent, more preferably from about 38 to about 44 mole percent, merunits derived from ethylene can be used to provide a film layer withexcellent barrier characteristics.

As mentioned previously, thermoplastic film material 12 can be amultilayer film. In such cases, one or more other layers are coextrudedor laminated to the surface of the meat-contact layer that is oppositethe meat product. Where a multilayer film is used, incorporation of alayer that includes an ethylene/vinyl acetate interpolymer can bepreferred.

A coextruded film that is preferred for certain applications has thegeneral structure A/B/C₁/D/C₂ /E where A is a meat-contact layer (asdescribed supra), B is a bulk layer, C₁ and C₂ are the same or differenttie layers, D is a barrier layer (as described supra), and E is a layerderived from ethylene/vinyl acetate interpolymer optionally blended witha polymer including mer units derived from ethylene (e.g., LLDPE). Wherelayers A and D are compatible (i.e., adhere well in the absence of a tielayer), layers B and/or C₁ optionally can be omitted. Likewise, wherelayers D and E are compatible, layer C₂ optionally can be omitted.

Various combinations of layers can be used in a multilayer film to beused as thermoplastic film material 12. Although 3- and 4-layerembodiments are preferred for many applications, such films also caninclude more or fewer layers. In general, thermoplastic film material 12can include from 1 to 15 layers, preferably from 1 to 10 layers, morepreferably from 2 to 10 layers, and even more preferably from 3 to 7layers.

Given below are a limited number of exemplary film structures in whichalphabetical symbols are used to represent various film layers:

A/B/C A/B/D A/C/B A/C/D A/D/B A/D/C A/D₁/D₂ A/B/C/D A/B/C/B A/B/D/BA/B/D/C A/B/D₁/D₂ A/C/B/D A/C/B/C A/C/B₁/B₂ A/C/D/B A/C/D₁/D₂

in which

“A” represents a meat-contact layer,

“B” represents a layer including at least one of a polyolefin,polystyrene, and polyurethane,

“C” represents a layer including one or more polymers that can provide alayer which has a low permeance to oxygen (preferably as describedsupra), and

“D” represents a layer including at least one of a polyester, polyamide,polypropylene, and polyurethane.

In the foregoing structures, preferred thicknesses of the various layersare as follows:

A, B, and D (independently): from about 1 to about 100 μm, preferablyfrom about 3 to about 50 μm, more preferably from about 4 to about 40μm, even more preferably from about 5 to about 40 μm, still morepreferably from about 7 to about 40 μm, yet more preferably from about 7to about 35 μm, and most preferably from about 10 to about 35 μm; and

C: from about 1 to about 50 μm, preferably from about 2 to about 50 μm,more preferably from about 3 to about 30 μm, even more preferably fromabout 4 to about 30 μm, still more preferably from about 4 to about 20μm, yet more preferably from about 4 to about 15 μm, and most preferablyfrom about 5 to about 15 μm.

Regardless of the structure of thermoplastic film material 12, one ormore conventional packaging film additives can be included therein.Examples of additives that can be incorporated in thermoplastic filmstructure 12 include, but are not limited to, antiblocking agents,antifogging agents, slip agents, colorants, flavorants, antimicrobialagents, meat preservatives, and the like. (The ordinarily skilledartisan is aware of numerous examples of each of the foregoing.) Wherethermoplastic film material 12 is to processed at high speeds, inclusionof one or more antiblocking agents in and/or on one or both outer layersof the film structure can be preferred. An example of a usefulantiblocking agent for certain applications is corn starch.

Envelope 10 is shown with three essentially linear sides. The verticalsides, 14 a and 14 b, here are shown in pleated, lay-flat form, althoughthis characteristic is merely optional. Vertical sides 14 a and 14 b areconnected by linear seal 16. Seal 16 can be formed by providingthermoplastic film material 12 in the form of (or forming it into) atube, applying a heated seal bar to the tube so as to form seal 16, thenslitting excess film material below seal 16 (not shown). By doing so,one can form a pouch into which can be filled with a predeterminedamount of meat product.

For the sake of simplicity and clarity, envelope 10 is shown as beingcompletely sealed but without any meat product enclosed therein. Inactual practice, however, contoured seal 18 normally is not formed untilsuch a meat product is introduced.

Contoured seal 18 includes five distinct segments 18 a-18 e. In FIG. 1,segments 18 a-18 e are delineated by boundaries 20 a-20 f although, inactual practice, such boundaries are not present on or in envelope 10.Likewise, each of segments 18 a-18 e is shown with a correspondingradius of curvature 24 a-24 e emanating from a corresponding imaginarycircle center 22 a-22 e. Circle centers 22 a-22 e and radii of curvature24 a-24 e are not present in actual practice; instead, they are shownand described here to simplify and clarify the description of segments18 a-18 e.

Segments 18 a-18 e define an imperfect arc, i.e., the arc does notdefine a smooth curve. Specifically, each of segments 18 a-18 e have aradius of curvature which differs from the radius (or radii) ofcurvature of the segment(s) which adjoin that particular segment.Although no two adjacent segments have identical radii of curvature, twoor more non-adjacent segments can have equivalent radii of curvature.For example, in FIG. 1, segments 18 a and 18 c have radii of curvature24 a and 24 c that are essentially identical in length to radii ofcurvature 24 b and 24 d for segments 18 b and 18 d, respectively.

Although envelope 10 can be of essentially any size (limited only by thesize of the equipment needed to make and process thermoplastic filmmaterial 12), it preferably is formed from a blown tube of thermoplasticfilm material 12 that has a lay flat widths of from about 1.5 to about50 cm, preferably from about 17.5 to about 37.5 cm, more preferably fromabout 20 to about 35 cm, and most preferably from about 22.5 to about32.5 cm. Additionally, each of radii of curvature 24 a-24 e,corresponding to segments 18 a-18 e respectively, preferably is no morethan about 2500 cm, more preferably no more than about 250 cm. In apreferred embodiment, at least two of radii of curvature 24 a-24 e areno more about 50 cm, even more preferably no more than about 25 cm. Inanother preferred embodiment, contoured seal 18 defines an arc of nomore than about 150 cm, preferably of no more than about 100 cm, morepreferably of no more than about 75 cm, even more preferably of no morethan about 50 cm, still more preferably of no more than about 40 cm, andmost preferably of no more than about 30 cm.

Contoured seal 18 can be formed by heat sealing the meat product-filledpouch (described supra) using a sealing jaw that has a shapecorresponding to contoured seal 18. Depending on the exact shape of thedistal ends of that jaw, the termini of contoured seal 18 (nearimaginary boundaries 20 a and 20 f) can be squared-off, irregular,rounded, etc., in shape. Once contoured seal 18 has been formed, excessthermoplastic film (not shown) can be trimmed away from envelope 10.

In forming envelope 10, the sealing jaws used to create seal 16 andcontoured seal 18 are maintained at an elevated temperature. The exacttemperature at which such jaws are maintained depends on the identity ofthe polymer(s) included in the layer(s) of thermoplastic film material12 involved in sealing. (Depending on whether a fin-type, lap-type, orbutt-type seal is used which, in turn, normally is determined by thetype of equipment on which the packaging process is performed, one orboth of the inside and outside layers of thermoplastic film material canbe involved. Preferably, both seal 16 and contoured seal 18 are fin-typeseals.) In general, sealing jaws can be maintained at a temperature inthe range of from about 120° to about 275° C., preferably from about150° to about 225° C., so as to produce strong, durable seals. (As thoseof ordinary skill in the art are aware, higher sealing jaw temperaturescan result in shorter contact times to induce sealing but also canresult in more defective seals due to adhesion of the polymer to thesealing jaw.)

Although the production of envelope 10 has been described by theformation of seal 16 followed by the formation of contoured seal 18, theorder in which the two seals are made can be reversed if so desired.

Although shown as essentially linear, seal 16 also can have a contouredshape, if desired. In this situation, the contour of seal 16 can be thesame as or different than that of contoured seal 18. Additionally, whereboth seals are contoured, one seal need not define an arc which includesat least four segments, i.e., can define an arc that includes two orthree segments.

As mentioned previously, the arc defined by a contoured seal of apackage according to the present invention can have as few as foursegments. Envelope 10 is shown with five such segments, and one ofordinary skill in the art easily can envision arcs with more than fivesegments. At present, those packages including a contoured seal whichdefines an arc having an odd number of segments are preferred with fivebeing a particularly preferred number of segments.

Turning now to FIG. 2, package 30 includes thermoplastic film material32 completely enclosing cooked meat product 34. To form package 30, ameat product is introduced into a pouch formed from a tube ofthermoplastic film material 32. (The pouch can be formed by creatingcross seal 38 in the tube and then cutting away excess film material, asdescribed supra.) Once the desired amount of meat product is added tothe pouch, contoured seal 36 can be created as described previously soas to form a meat-containing envelope. As described previously, seals 36and 38 can be formed in reverse order as just described and both ofseals 36 and 38 can be contoured.

After the filled envelope is created, it is heated so as to cook themeat product. This cooking step is performed at a temperature up toabout the Vicat softening point of the meat-contact layer polymer thatincludes mer units derived from a C₂-C₄ α-olefin polymer. The cookingstep preferably is performed at a temperature of from about 50° to about100° C., more preferably from about 60° to about 95° C., even morepreferably from about 65° to about 90° C., and most preferably fromabout 70° to about 90° C.

During the cooking process, the meat product conforms to the shape ofthe envelope. As mentioned previously, this shape advantageously has thegeneral appearance of a poultry breast. Accordingly, a preferred type ofmeat product includes poultry meat, particularly chicken and/or turkeybreast meat.

In practice, packages of the type of package 30 typically weigh fromabout 1 to about 20 kg, more typically from about 2 to about 15 kg, andeven more typically from about 2.5 to about 10 kg.

FIG. 3 illustrates a cross sectional view of package 30 from FIG. 2taken along section line 3—3. In FIG. 3, package 40 includesthermoplastic film material 42 completely enclosing cooked meat product44. Seals 46 and 48 correspond, respectively, to seals 36 and 38 fromFIG. 2. Cooked meat product 44 is prepared according to the heatingprocedure described supra.

Various modifications and alterations that do not depart from the scopeand spirit of this invention will become apparent to those skilled inthe art. This invention is not to be unduly limited to the illustrativeembodiments set forth herein.

We claim:
 1. A method of forming a packaged, cooked food productcomprising: enclosing a food product within a package comprising athermoplastic, heat-shrinkable film having a total free shrink at 85° C.of at least about 2% and comprising an inside layer comprising a polymercomprising mer units derived from a C₂-C₄ α-olefin, said package havingat least one seal which defines an arc, said arc comprising at leastfour segments, each of said segments having a radius of curvaturediffering from the radius of curvature of any adjoining segment; andsubsequently heating the packaged food product to shrink the film and tocook said food product to form a packaged, cooked food productconforming to the shape of the package.
 2. The method of claim 1 whereinthe food product comprises meat.
 3. The method of claim 2 wherein saidfilm further comprises a barrier layer with an oxygen permeance of nomore than about 150 cm³/m².atm.24 hours at about 23° C. and 0% relativehumidity.
 4. The method of claim 1 wherein said arc comprises at leastfive segments.
 5. The method of claim 4 wherein each of said segmentshas a radius of curvature of no more than about 2500 cm.
 6. The methodof claim 5 wherein each of said segments has a radius of curvature of nomore than about 250 cm.
 7. The method of claim 6 wherein at least two ofsaid segments have radii of curvature of no more than about 50 cm. 8.The method of claim 7 wherein at least two of said segments have radiiof curvature of no more than about 25 cm.
 9. The method of claim 8wherein said inside layer has a surface energy of at least about 0.0325J/m².
 10. The method of claim 9 wherein said surface energy is at leastabout 0.0350 J/m².
 11. The method of claim 9 wherein said surface energyis at least about 0.0450 J/m².
 12. The method of claim 1 wherein saidpolymer has a Vicat softening point of at least about 70° C.
 13. Themethod of claim 12 wherein said Vicat softening point is at least about95° C.
 14. The method of claim 1 wherein said film has a shrink tensionof at least about 700 kPa at 85° C.
 15. The method of claim 1 whereinsaid C₂-C₄ α-olefin comprises propylene.
 16. The method of claim 1wherein said polymer comprising mer units derived from a C₂-C₄ α-olefinfurther comprises mer units derived from one or more of at least oneC₆-C₁₂ α-olefin, a C₃-C₁₈ ethylenically unsaturated ester, and a C₃-C₁₈ethylenically unsaturated acid.
 17. The method of claim 1 wherein: thefilm comprises: an inside layer comprising at least 10 weight percent ofa copolymer selected from ethylene/α-olefin copolymer andpropylene/α-olefin, said copolymer having at least 2 weight percent merunits derived from a C₃-C₁₈ ethylenically unsaturated acid, wherein saidcopolymer has a Vicat softening point “V” in ° C., of V>111° C.-2.78°C.(m _(A)) where m_(A) is the weight percent of mer units in saidcopolymer derived from said C₃-C₁₈ ethylenically unsaturated acid withm_(A) ranging from about 2 to about 25, inclusive, and a barrier layerwith an oxygen permeance of no more than about 150 cm³/m².atm.24 hoursat 23° C. and 0% relative humidity, said barrier layer comprising apolymer selected from ethylene/vinyl alcohol copolymer, ethylene/vinylacetate copolymer, and ethylene/vinyl acetate copolymer; said film has asurface energy of at least about 0.0325 J/m², a shrink tension of atleast about 700 kPa at 85° C.; and said arc comprises at least fivesegments, each of said segments having a radius of curvature differingfrom the radius of curvature of any adjoining segment, each of saidsegments having a radius of curvature of no more than about 2500 cm. 18.The method of claim 17 wherein said copolymer comprisespropylene/α-olefin copolymer.
 19. The method of claim 1 wherein said arccomprises at least five segments, each having a radius of curvature ofno more than about 2500 cm and said film has a shrink tension of atleast about 700 kPa at 85° C.
 20. The method of claim 1 wherein theinside layer comprises at least 10 weight percent of an interpolymercomprising mer units derived from at least one C₂-C₄ α-olefin and atleast about 2 weight percent mer units derived from at least one C₃-C₁₈unsaturated acid.
 21. The method of claim 20 wherein said interpolymerhas a Vicat softening point, V, of V>111° C.-2.78° C.(m _(A)) wherem_(A) is the percent of mer units in said copolymer derived from saidC₃-C₁₈ ethylenically unsaturated acid with m_(A) ranging from about 2 toabout 25, inclusive.
 22. The method of claim 21 wherein m_(A) rangesfrom about 4 to about 15, inclusive.
 23. The packaged, cooked foodproduct formed by the method of claim
 1. 24. The method of claim 1wherein the thermoplastic, heat-shrinkable film has a free shrink at 85°C. in at least one direction of at least 5%.
 25. The method of claim 1wherein the thermoplastic, heat-shrinkable film has a free shrink at 85°C. in at least one direction of at least 10%.